The 5H4 antibody reacts with mouse CD122, the 90-110 kDa interleukin-2 receptor beta chain. CD122 is expressed by NK cells and some T cells in the periphery and is upregulated by activation. CD122 associates with CD25 and CD132 (common gamma chain) to form the high affinity IL-2 receptor. Binding of IL-2 to CD122 is not inhibited by the 5H4 antibody.